JP2009104974A - Positive electrode active material for non-aqueous secondary battery, method for producing the same, and non-aqueous secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode active material having a large charge and discharge capacity and superior thermal stability of particles, and excellent mass-producibility, and a nonaqueous secondary battery. <P>SOLUTION: The cathode active material for the nonaqueous secondary battery is composed of a compound oxide of lithium, sodium, and nickel, and has an electron structure in which, when measured by using an X band and at temperatures 200-300 K, a primary differential absorption spectrum of electron spin resonance is observed, and the relations of the line width (ΔH<SB>pp</SB>) between the peaks and the measurement temperature (T), that is, dΔHpp/dT is less than 0.5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a positive electrode active material for a non-aqueous secondary battery, a method for producing the same, and a non-aqueous secondary battery using the same, and particularly relates to a suitable composite oxide of lithium, sodium, and nickel.

  In recent years, electronic devices have become increasingly portable and cordless, and there is an increasing demand for secondary batteries that are small and lightweight and have a high energy density as power sources for driving these devices. In addition to small-sized consumer applications, technological developments for large-sized secondary batteries that require long-term durability and safety, such as power storage and electric vehicles, are also accelerating.

  From this point of view, non-aqueous secondary batteries, in particular lithium secondary batteries, are expected to be used as power sources for electronic devices, for power storage, and for electric vehicles because they have high voltage and high energy density. Yes.

A non-aqueous secondary battery includes a positive electrode, a negative electrode, and a separator interposed therebetween, and a polyolefin microporous film is mainly used as the separator. As the non-aqueous electrolyte, a liquid non-aqueous electrolyte (non-aqueous electrolyte) in which a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an aprotic organic solvent is used. Further, as the positive electrode active material, lithium cobalt oxide (for example, LiCoO ₂ ), which has a high potential with respect to lithium, is excellent in safety, and is relatively easy to synthesize, is used. As the negative electrode active material, various carbon materials such as graphite are used. A non-aqueous secondary battery using a battery has been put into practical use.

Under such circumstances, attempts to put lithium nickel oxide (for example, LiNiO ₂ ) into practical use are also active from the viewpoint of further increasing the capacity compared to lithium cobalt oxide. However, although lithium nickel oxide has a high capacity, it has low crystal stability and has problems in cycle characteristics and thermal stability. Therefore, the following proposals have been made.

  For example, for the purpose of improving cycle characteristics, a method for optimizing the particle structure of the active material has been proposed (see, for example, Patent Document 1).

  According to this proposal, it is stated that the cycle characteristics can be improved because the primary particle diameter of the positive electrode active material is increased.

  Moreover, in order to obtain a high capacity lithium nickel composite oxide, a method of optimizing the heat treatment conditions of the active material has been proposed (see, for example, Non-Patent Document 1).

  According to this proposal, it is stated that a high-capacity lithium-nickel composite oxide can be obtained by suppressing the exchange reaction (disorder) between lithium and divalent nickel in the lithium layer.

  Furthermore, a method for synthesizing an active material with less disorder by adding sodium to a lithium nickel composite oxide has been proposed (see, for example, Non-Patent Document 2).

According to this proposal, it is stated that an active material with less disorder can be synthesized by adding about 0.85 sodium.
JP 2001-85006 A H. Arai et al., “Characterization and cathode of performance of Li1-xNi1 + xO2 prepared with the ex- Solid State Ionics, UK, Elsevier Science BV, 1995, 80, p261-269 Tadaaki Matsumura and 5 others, “Synthesis, structure and physical properties of Li1-xNa1 + xNiO2”, Solid State Io (Sonic UK) Elsevier Science Bee, Elsevier Science BV, 2002, 152-153, p303-309 C. Julien et al., “LiM1-yM′yO2 (M = Ni, Co, M ′ = Mg, Al, B) Electrochemical properties of LiM1-yM′yO2 (M = Ni , Co,; M ′ = Mg, Al, B)) ”, Solid State Ionics, UK, Elsevier Science BV, 2000, Vol. 135, p121- 130

  However, even if the technique proposed in Patent Document 1 is used, heat treatment is performed at a temperature of 900 ° C., and there is a problem that the charge / discharge capacity is small.

  Moreover, even if the technique proposed in Non-Patent Document 1 is used, heat treatment is performed at a temperature of 700 ° C., the primary particle size is small, and there is a problem with the thermal stability of the positive electrode active material in a charged state. Had.

Furthermore, even when the technique proposed in Non-Patent Document 2 is used, Li _0.15 Na _0.85 NiO ₂ is easily affected by moisture in the atmosphere and must be handled in an argon atmosphere. That is, in order to assemble a non-aqueous secondary battery using the synthesized active material, a large amount of argon gas has to be used, which has a problem of increasing costs.

  Therefore, the present invention solves the above-mentioned conventional problems, a positive electrode active material having a large charge / discharge capacity and excellent particle thermal stability and mass productivity, a method for producing the same, and a non-aqueous secondary battery using the positive electrode active material The purpose is to provide.

In order to solve the conventional problems, the present invention measures an electron spin resonance at a temperature of 200 to 300 K using an X band in a positive electrode active material for a non-aqueous secondary battery made of a composite oxide of lithium, sodium and nickel. The first-order absorption spectrum of electron spin resonance is observed, and the electronic structure in which dΔH _pp / dT, which is the relationship between the line width (ΔH _pp ) between the peaks and the measurement temperature (T), is less than 0.5 is obtained. This is a positive electrode active material for a non-aqueous secondary battery.

  Here, the X band is a kind of microwave and is an electromagnetic wave having a frequency of 9.4 GHz and a wavelength of about 3 cm.

  By using the positive electrode active material of the present invention, a lithium secondary battery having a large charge / discharge capacity can be produced. Moreover, since it becomes strong against moisture, it can be handled in an atmosphere of dry air instead of argon gas.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material and non-aqueous secondary battery which are large in charging / discharging capacity | capacitance and excellent in the thermal stability and mass productivity of particle | grains can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described.

In the present invention, as described above, when the X band is used and measurement is performed at a temperature of 200 to 300 K, a first-order differential absorption spectrum of electron spin resonance is observed, and the line width (ΔH _pp ) between the peaks and the measurement temperature ( It was found that a lithium secondary battery having a large charge / discharge capacity can be obtained by using a lithium nickel composite oxide characterized by having an electronic structure in which dΔH _pp / dT, which is a relationship of T), is 0.5 or less. It is a thing. The reason is considered as follows.

In electron spin resonance measurement of lithium nickel composite oxide, in the paramagnetic region below room temperature, the line width between peaks narrows with cooling due to the influence of the magnetic dipole action of divalent nickel. In other words, the smaller the value of dΔH _pp / dT, which is the relationship between the line width (ΔH _pp ) between the peaks of the electron resonance spectrum of the lithium nickel composite oxide and the measurement temperature (T), is included in the lithium nickel composite oxide. This indicates that the amount of valent nickel is small.

Divalent nickel causes a disorder with lithium in the lithium layer and inhibits the electrochemical reaction of lithium ions. For this reason, since the charge / discharge capacity is greatly reduced, it is not preferable that the value of dΔH _pp / dT is larger than 0.5.

  Further, in the method for producing a positive electrode active material for a non-aqueous secondary battery according to the present invention, a positive electrode active material for a non-aqueous secondary battery comprising a step of mixing and heat-treating a precursor oxide, a lithium compound and sodium peroxide. Manufacturing Method Use of a positive electrode active material is preferable in that a single-phase lithium nickel composite oxide can be obtained.

  In the present invention, sodium peroxide acts as a so-called sintering accelerator. With other sodium compounds, such effects are small.

  It is known that a single-phase lithium-nickel composite oxide cannot be obtained with boron or the like, which is a general sintering accelerator (Non-patent Document 3).

  The primary particle diameter of the lithium nickel composite oxide is preferably 1 μm or more. When the primary particle diameter is 1 μm or less, the specific surface area is increased, and the thermal stability of the positive electrode active material during charging is undesirably reduced. Further, primary particles of 4 μm or more are difficult to synthesize, and even if synthesized, the result of electron spin resonance tends to be 0.5 or more.

The composition of the positive electrode active material for a nonaqueous secondary battery of the present invention is _{Li 1-x Na x Ni 1} -y Me y O 2 (0 ≦ x ≦ 0.05,0 ≦ y ≦ 0.34, Me is Co, Preferably, it is at least one element selected from the group consisting of Fe, Cu, Al, Mg, Ti, Zr, Ce, and Y). Since sodium in the lithium site does not participate in the charge / discharge mechanism, if the value of x exceeds 0.05, the charge / discharge capacity decreases, which is not preferable.

As a manufacturing method of the positive electrode active material, the amount of sodium peroxide (Na) added is 0 <Na / (Li + Na) ≦ 0.05 in terms of molar ratio with respect to lithium (Li) of the lithium compound to be mixed at the same time. Is preferred. That is, it is preferable to satisfy the relational expression Li _1-x Na _x (where 0 <x ≦ 0.05).

  This is because the synthesized positive electrode active material can be handled in dry air at −40 ° C. with the above addition amount. Moreover, the primary particle diameter of the positive electrode active material increases by increasing the amount of sodium added. However, if the molar ratio exceeds 0.05, the charge / discharge capacity of the active material decreases, which is not preferable.

  The heat treatment temperature during the synthesis of the lithium nickel composite oxide is preferably 700 ° C. to 800 ° C. When the heat treatment temperature is lower than 700 ° C., the primary particles are hardly sintered. When the heat treatment temperature is higher than 800 ° C., the Li / Ni ratio decreases and the Li / Ni disorder increases. The heat treatment time is preferably 3 to 30 hours, although it depends on the synthesis temperature. And it is preferable to perform said heat processing in oxygen atmosphere.

  The non-aqueous secondary battery of the present invention is characterized by the positive electrode active material, and other components are not particularly limited.

  The positive electrode is usually composed of a positive electrode current collector and a positive electrode mixture supported thereon. The positive electrode mixture can contain a binder, a conductive agent and the like in addition to the positive electrode active material. The positive electrode is produced, for example, by mixing a positive electrode mixture composed of a positive electrode active material and an optional component with a liquid component to prepare a positive electrode mixture slurry, applying the obtained slurry to a positive electrode current collector, and drying. Similarly, the negative electrode is prepared by mixing a negative electrode mixture composed of a negative electrode active material and an optional component with a liquid component to prepare a negative electrode mixture slurry, applying the obtained slurry to a negative electrode current collector, and drying the mixture. .

As the negative electrode active material of the non-aqueous secondary battery of the present invention, for example, metals, metal fibers, carbon materials, oxides, nitrides, tin compounds, silicon compounds, various alloy materials, and the like can be used. Examples of the carbon material include carbon materials such as various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, and amorphous carbon. In addition, a simple substance such as silicon (Si) or tin (Sn), or a silicon compound or tin compound such as an alloy, a compound, or a solid solution is preferable from the viewpoint of a large capacity density. For example, as a silicon compound, SiO _x (0.05 <x <1.95), or any of these may be B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, An alloy, a compound, a solid solution, or the like in which a part of Si is substituted with at least one element selected from the group consisting of Ta, V, W, Zn, C, N, and Sn can be used. As the tin compound, Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (0 <x <2), SnO ₂ , SnSiO ₃ or the like can be applied. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

Examples of the positive electrode or negative electrode binder include PVDF, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, and polyethyl acrylate. Ester, Polyacrylic acid hexyl ester, Polymethacrylic acid, Polymethacrylic acid methyl ester, Polymethacrylic acid ethyl ester, Polymethacrylic acid hexyl ester, Polyvinyl acetate, Polyvinylpyrrolidone, Polyether, Polyethersulfone, Hexafluoropolypropylene, Styrene Butadiene rubber, carboxymethyl cellulose, etc. can be used. Two types selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene A copolymer of the above materials may be used. Two or more selected from these may be mixed and used. Examples of the conductive agent contained in the electrode include natural graphite and artificial graphite graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and other carbon blacks, carbon fibers and metal fibers. Conductive fibers such as carbon fluoride, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, organic conductive materials such as phenylene derivatives, etc. Is used.

The blending ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 97% by weight of the positive electrode active material, 1 to 20% by weight of the conductive agent, and 1 to 10% by weight of the binder.
In addition, the mixing ratio of the negative electrode active material and the binder is desirably 93 to 99% by weight of the negative electrode active material and 1 to 10% by weight of the binder, respectively.

  For the current collector, a long porous conductive substrate or a nonporous conductive substrate is used. As a material used for the conductive substrate, as the positive electrode current collector, for example, stainless steel, aluminum, titanium, or the like is used. As the negative electrode current collector, for example, stainless steel, nickel, copper, or the like is used. Although the thickness of these electrical power collectors is not specifically limited, 1-500 micrometers is preferable and 5-20 micrometers is more desirable. By setting the thickness of the current collector within the above range, it is possible to reduce the weight while maintaining the strength of the electrode plate.

  As the separator interposed between the positive electrode and the negative electrode, a microporous thin film, a woven fabric, a non-woven fabric, etc. having a large ion permeability and having a predetermined mechanical strength and an insulating property are used. As the material of the separator, for example, polyolefin such as polypropylene and polyethylene is preferable from the viewpoint of safety of the non-aqueous secondary battery because it has excellent durability and has a shutdown function. The thickness of the separator is generally 10 to 300 μm, but is desirably 40 μm or less. Moreover, it is more preferable to set it as the range of 15-30 micrometers, and the range of the more preferable separator thickness is 10-25 micrometers. Furthermore, the microporous film may be a single layer film made of one kind of material, or a composite film or a multilayer film made of one kind or two or more kinds of materials. Further, the porosity of the separator is preferably in the range of 30 to 70%. Here, the porosity indicates the volume ratio of the pores to the separator volume. A more preferable range of the porosity of the separator is 35 to 60%.

  As the non-aqueous electrolyte, a liquid, gel, or solid (polymer solid electrolyte) substance can be used.

  A liquid non-aqueous electrolyte (non-aqueous electrolyte) is obtained by dissolving an electrolyte (for example, a lithium salt) in a non-aqueous solvent. The gel-like non-aqueous electrolyte includes a non-aqueous electrolyte and a polymer material that holds the non-aqueous electrolyte. As this polymer material, for example, polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, polyvinylidene fluoride hexafluoropropylene and the like are preferably used.

  As the non-aqueous solvent for dissolving the electrolyte, a known non-aqueous solvent can be used. Although the kind of this non-aqueous solvent is not specifically limited, For example, cyclic carbonate ester, chain | strand-shaped carbonate ester, cyclic carboxylic acid ester etc. are used. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

Examples of the electrolyte dissolved in the non-aqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , and lower aliphatic carboxylic acid. Lithium acid, LiCl, LiBr, LiI, chloroborane lithium, borates, imide salts, and the like can be used. Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ') and bis (2,3-naphthalenedioleate (2-)-O, O') boric acid. Lithium, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate Etc. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ), Lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), and the like. One electrolyte may be used alone, or two or more electrolytes may be used in combination.

  In addition, the non-aqueous electrolyte may contain a material that can be decomposed on the negative electrode as an additive to form a film having high lithium ion conductivity and increase charge / discharge efficiency. Examples of the additive having such a function include vinylene carbonate (VC), 4-methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4-ethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, 4-propyl. Examples include vinylene carbonate, 4,5-dipropyl vinylene carbonate, 4-phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), and divinyl ethylene carbonate. These may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, and divinyl ethylene carbonate is preferable. In the above compound, part of the hydrogen atoms may be substituted with fluorine atoms. The amount of electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2 mol / L.

  Further, the non-aqueous electrolyte may contain a known benzene derivative that decomposes during overcharge to form a film on the electrode and inactivate the battery. As the benzene derivative, those having a phenyl group and a cyclic compound group adjacent to the phenyl group are preferable. As the cyclic compound group, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, a phenoxy group, and the like are preferable. Specific examples of the benzene derivative include cyclohexylbenzene, biphenyl, diphenyl ether and the like. These may be used alone or in combination of two or more. However, the content of the benzene derivative is preferably 10% by volume or less of the entire non-aqueous solvent.

  Hereinafter, the present invention will be described based on examples.

(Example 1)
(I) Production of Positive Electrode Active Material Ni _0.81 Co _0.16 Al _0.03 O (hereinafter referred to as NCAO), which is a precursor oxide, and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: The mixture was mixed at a ratio of Na ₂ O ₂ = 1: 1: 0.005, and heat treatment was performed at 750 ° C. for 5 hours in an oxygen atmosphere. Thereafter, the active material was synthesized by grinding in a mortar. From the ICP analysis, the ratio of each element was Li: Na: Ni: Co: Al = 99: 1: 81: 16: 3. An SEM image of the obtained active material is shown in FIG. Secondary particles composed of primary particles having an average particle diameter of about 1 μm were obtained. The size of the obtained secondary particles was about 10 μm. FIG. 2 shows a first-order differential absorption spectrum when the electron spin resonance of the synthesized active material is measured at a temperature of 300 K using the X band. From the peak of the obtained spectrum, ΔH _pp indicated by 1 which is the line width between peaks was obtained.

Similarly, measurement was performed at a temperature of 200 to 300 K, and the line width between the peaks was obtained. DΔH _pp / dT, which is the relationship between the line width between peaks (ΔH _pp ) and the measurement temperature (T), has a linear relationship as shown in 2 of FIG. 3, and the dΔH _pp / dT is 0.22 mTK ⁻¹ . there were.

(II) Production of positive electrode plate 100 parts by weight of the positive electrode active material, 4 parts by weight of acetylene black as a conductive agent, and 5 parts by weight of polyvinylidene fluoride as a binder in a solvent of N-methylpyrrolidone (NMP) ( PVDF) was mixed with a solution to obtain a paste containing a positive electrode mixture. This paste was applied on both sides of a 15 μm thick aluminum foil serving as a current collector, dried, rolled, and cut into a predetermined size to obtain a positive electrode plate.

(III) Production of Negative Electrode Plate 75 parts by weight of artificial graphite powder was mixed with 20 parts by weight of acetylene black as a conductive agent and 5 parts by weight of polyvinylidene fluoride resin as a binder, and these were dehydrated N-methyl-2 -A slurry-like negative electrode mixture was prepared by dispersing in pyrrolidone. This negative electrode mixture was applied to both surfaces of a negative electrode current collector made of copper foil, dried, rolled, and cut into predetermined dimensions to obtain a negative electrode plate.

(IV) Preparation of non-aqueous electrolyte solution 1 wt% vinylene carbonate was added to a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3, and LiPF ₆ was dissolved at a concentration of 1.0 mol / L. A water electrolyte was obtained.

(V) Battery assembly The positive electrode sheet and the negative electrode sheet were cut into a size of 35 mm x 35 mm, and ultrasonically welded to an aluminum plate with a lead and a copper plate, respectively. The aluminum plate and the copper plate were taped and integrated so that each electrode sheet was opposed to the PP microporous membrane separator. Next, this integrated product was placed in a cylindrical aluminum laminated bag having both ends open, and one opening of the bag was welded at the lead portion. And the electrolyte solution prepared from the other opening part was dripped.
The battery assembled in this manner was charged with a current of 0.1 mA for 1 hour, then deaerated at 10 mmHg for 10 seconds, and the poured opening was sealed by welding. Then, preliminary charging / discharging was performed 5 times at a constant current of 7 mA while the upper limit voltage was 4.2 V and the lower limit voltage was 3.0 V. This is referred to as the battery of Example 1.

(Example 2)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.015. A battery produced in the same manner as in Example 1 except that it was mixed was designated as Example 2. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 97: 3: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 2 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.37 mTK ⁻¹ .

(Example 3)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.025. A battery produced in the same manner as in Example 1 except that it was mixed was designated as Example 3. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 95: 5: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 3 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.47 mTK ⁻¹ .

Example 4
The positive electrode active material is composed of the precursor oxides NCAO, LiOH.H ₂ O, and Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.05. A battery produced in the same manner as in Example 1 except for mixing was designated as Example 4. From the ICP analysis, the element ratio was Li: Na: Ni: Co: Al = 90: 10: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 4 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.49 mTK ⁻¹ .

(Example 5)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.015. A battery produced in the same manner as in Example 1 except that it was mixed and fired at 700 ° C. for 5 hours in an oxygen atmosphere was designated as Example 5. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 97: 3: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 1 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.34 mTK ⁻¹ .

(Example 6)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.015. A battery produced in the same manner as in Example 1 except that it was mixed and baked at 800 ° C. for 5 hours in an oxygen atmosphere was designated as Example 6. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 97: 3: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 3 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.41 mTK ⁻¹ .

(Example 7)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.015. A battery produced in the same manner as in Example 1 except that it was mixed and baked in an oxygen atmosphere at 750 ° C. for 30 hours was designated as Example 7. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 97: 3: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 2 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.39 mTK ⁻¹ .

(Example 8)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.001. A battery produced in the same manner as in Example 1 except for mixing was designated as Example 8. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 99.9: 0.2: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 0.4 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.21 mTK ⁻¹ .

(Comparative Example 1)
The positive electrode active material was mixed with the precursor oxide NCAO and LiOH.H ₂ O at a molar ratio of NCAO: LiOH.H ₂ O = 1: 1, and baked at 900 ° C. for 5 hours in an oxygen atmosphere. A battery manufactured in the same manner as in Example 1 was referred to as Comparative Example 1. From the ICP analysis, each element ratio was Li: Ni: Co: Al = 100: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 4 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.66 mTK ⁻¹ . In FIG. 3, the relationship of Comparative Example 1 is indicated by 3.

(Comparative Example 2)
The positive electrode active material is a precursor oxide of NCAO and LiOH.H ₂ O, Na ₂ O ₂ in a molar ratio of NCAO: LiOH.H ₂ O: Na ₂ O ₂ = 1: 1: 0.015. A battery produced in the same manner as in Example 1 except that it was mixed and fired in an oxygen atmosphere at 900 ° C. for 5 hours was designated as Comparative Example 2. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 97: 3: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 4 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.67 mTK ⁻¹ .

(Comparative Example 3)
A positive electrode active material was prepared in the same manner as in Example 1 except that the precursor oxide NCAO and LiOH · H ₂ O were mixed at a molar ratio of NCAO: LiOH · H ₂ O = 1: 1. The battery was referred to as Comparative Example 3. From the ICP analysis, each element ratio was Li: Ni: Co: Al = 100: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 0.2 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.21 mTK ⁻¹ .

(Comparative Example 4)
The positive electrode active material was mixed with the precursor oxide NCAO, LiOH.H ₂ O, and NaHCO ₃ in a molar ratio of NCAO: LiOH · H ₂ O: NaHCO ₃ = 1: 0.97: 0.03. A battery manufactured in the same manner as in Example 1 was referred to as Comparative Example 3. From the ICP analysis, the respective element ratios were Li: Na: Ni: Co: Al = 97: 3: 81: 16: 3. Secondary particles composed of primary particles having an average particle diameter of about 0.2 μm were obtained. The size of the obtained secondary particles was about 10 μm. When electron spin resonance was measured under the same measurement conditions as in Example 1, dΔH _pp / dT of electron spin resonance was 0.39 mTK ⁻¹ .

(VI) Battery Evaluation For Examples 1 to 8 and Comparative Examples 1 to 3, the upper limit voltage is 4.2 V and the lower limit voltage is about 25 hours at ambient temperature and a constant current (12 mA) of about 1 hour at room temperature. Charging / discharging was repeated between 3.0V. The charge / discharge capacity at the first cycle is shown in Table 1.

(VII) Evaluation of thermal stability Differential calorimetry was performed under the coexistence of the positive electrode and the electrolyte during charging, and the calorific value thereof was examined. This is for confirming that according to the positive electrode active material of the present invention, the reactivity with the electrolytic solution is reduced and the thermal stability of the positive electrode active material can be improved. The measurement conditions for this differential calorimetry are as follows: after charging the battery to 4.2 V, disassemble the battery in a dry air atmosphere with a dew point of −40 ° C., take out the positive electrode, wash it with ethyl methyl carbonate, depressurize the ethyl methyl carbonate. Then, an unused electrolytic solution was added to a predetermined amount (1 mg) of the positive electrode mixture, and molded into a pressure-type differential calorimetric analysis cell. In the differential calorimetry, the cell was heated from room temperature to 300 ° C. at a heating rate of 10 Kmin ⁻¹ , the change in differential calorific value at that time was examined, and the peak shape is shown in FIG. In FIG. 4, 4 is Example 1 and 5 is Comparative Example 3. The maximum peak value is shown in Table 1. The maximum value of the peak represents the intensity of heat generation of the active material, and it is considered that the smaller the maximum value of the peak, the better the active material is in thermal stability.

As shown in Table 1, in Examples 1 to 3 and Examples 5 to 7 of the present invention, the charge / discharge capacity was 170 mAhg ⁻¹ or more, and the charge / discharge capacity was large. On the other hand, Example 4 had a small charge / discharge capacity of 167 mAhg ⁻¹ . This is thought to be due to a decrease in charge / discharge capacity due to a decrease in the amount of lithium involved in charge / discharge by increasing the amount of sodium added. Therefore, in order to obtain a large charge / discharge capacity, the amount of sodium added is preferably 0 <Na / (Li + Na) ≦ 0.05. Then, dΔH _pp / dT of Examples 1-8 was less than 0.5.

On the other hand, Comparative Examples 1 and 2 each had a small charge and discharge capacity of 140 mAhg ⁻¹ or less. dΔH _pp / dT reflects the amount of divalent nickel in the lithium-nickel composite oxide, and in the lithium-nickel composite oxides of Comparative Examples 1 and 2 and the lithium-nickel composite oxides of Examples 1 to 7. There is a difference in the amount of divalent nickel, which is considered unsuitable for the charge / discharge mechanism.

When Examples 1-7 are compared with Comparative Example 3, it can be seen that the differential thermal analysis values of Examples 1-7 are greatly reduced. This is thought to be because the addition of sodium peroxide increased the primary particle size and reduced the specific surface area, thereby suppressing the reaction with the electrolyte and improving the thermal stability of the active material. On the other hand, in Example 8, the amount of sodium peroxide added was not sufficient, the primary particle size did not increase, and the specific surface area was large, so the reaction with the electrolytic solution was not suppressed. In Comparative Example 4, it was considered that even when sodium hydrogen carbonate was used as the sodium source, the primary particle size did not increase, so that the reaction with the electrolytic solution was not suppressed, and the thermal stability of the active material was not improved. That is, in order to increase the primary particle diameter of the lithium nickel composite oxide, it is considered necessary to add sodium peroxide as a sodium source. From the above results, it was possible to improve the thermal stability of the active material while maintaining the charge / discharge capacity by adding sodium peroxide.

  In the above embodiment, a cylindrical aluminum laminate type battery is used, but the same effect can be obtained by using a battery having a different shape such as a square type.

SEM photograph of the active material of the present invention First-order differential absorption spectrum of electron spin resonance of the active material of the present invention at a temperature of 300K Shows the relationship between the line width between peaks obtained from the primary differential absorption spectrum of electron spin resonance of the present invention the active material ([Delta] H _pp) and measured temperature (T) Diagram of differential calorimetry of the active material of the present invention

Explanation of symbols

1 Line width between peaks (ΔH _pp )
The line width between the 2 Example 1 peak ([Delta] H _pp) and differential relationship 4 Example 1 of line width between peaks of relations 3 Comparative Example 1 measured temperature (T) ([Delta] H _pp) and measured temperature (T) Calorimetry results 5 Differential calorimetry results of Comparative Example 3

Claims (6)

A positive electrode active material for a non-aqueous secondary battery comprising a composite oxide of lithium, sodium, and nickel, when the electron spin resonance is measured at a temperature of 200 to 300 K using the X band for the composite oxide A positive electrode active material for a non-aqueous secondary battery in which a first-order differential absorption spectrum peak of electron spin resonance is observed and the relational expression (1) is satisfied.
dΔH _pp /dT<0.5 (where ΔH _pp is the line width between the peaks and T is the measured temperature) (1)   2. The positive electrode active material for a non-aqueous secondary battery according to claim 1, wherein the composite oxide has a primary particle size of 1 μm to 4 μm. The composite oxide has a general formula Li _1-x Na _x Ni _1-y Me _y O ₂ (where 0 <x ≦ 0.05, 0 ≦ y ≦ 0.34, Me represents Co, Fe, Cu Or at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ce, and Y). The positive electrode active material for a non-aqueous secondary battery according to claim 1, .   A method for producing a positive electrode active material for a non-aqueous secondary battery according to claim 1, wherein the precursor oxide, the lithium compound, and sodium peroxide are mixed and heat-treated. The manufacturing method of the positive electrode active material for non-aqueous secondary batteries containing. The amount of lithium in the lithium compound and the amount of sodium in the sodium peroxide satisfy the relational expression (2), and a heat treatment temperature in the heat treatment step is set to 700 ° C or more and 800 ° C or less. A method for producing a positive electrode active material for an aqueous secondary battery.
Li _1-x Na _x (where 0 <x ≦ 0.05) (2)   A battery comprising a positive electrode plate using the positive electrode active material according to any one of claims 1 to 3, a negative electrode plate using a negative electrode active material capable of occluding and releasing lithium, and a separator together with a non-aqueous electrolyte. A non-aqueous secondary battery enclosed in a case.